In the oilfield it has become common practice to drill a well that intersects numerous formations or portions of formations. Sometimes the well may be primarily vertical and sometimes the well may have a significant horizontal section. Once the wellbore has been drilled it is usually necessary to case the well. In the past the casing was typically a number of joints of solid pipe joined together and then run into the wellbore. Once the casing had been located in the wellbore it was then cemented in place by forcing cement through the interior of the pipe, out of the toe of the pipe, and back up around the annular area formed between the casing and the wellbore itself.
With the casing cemented in the well the interior of the pipe casing was effectively sealed from allowing any fluids to flow from the formations to the interior. With the casing effectively sealed against fluid flow it is then necessary to provide a means to access the exterior of the casing and reestablish fluid flow upon demand. Typically the casing is perforated or a ported sleeve is used to reestablish fluid flow with the exterior the casing. The ported sleeve is commonly referred to as a toe sleeve. Because positive fluid flow through the casing is limited at best without access to the exterior of the casing, it is difficult to pump a ball or a dart through the casing to actuate the toe sleeve. Therefore toe sleeve actuation is limited to pressure actuation or mechanical manipulation from the surface such as the use of slick line or electric line. Today many toe sleeves are actuated by pressure. Unfortunately there may be other requirements to pressurize the casing prior to actuating the toe sleeve. For instance it may be necessary to check the integrity of the casing and the cement holding the casing in place by performing a pressure test on the casing. In such instances it is not uncommon to pressurize the casing to 10,000 psi or more. Any toe sleeve actuation greater than the pressure test creates uncertainty as to whether the toe sleeve actuated or the casing failed.